The development of renewable biofuels, such as bio-ethanol [1], butanol [2], bio-diesel [3-5] and jetfuels [6], helps to address energy security and climate change concerns. For economically industrial production of biofuels, titers and yield of biofuels synthesis must be sufficiently high. However biofuels are frequently toxic to cells, thereby placing a limit on the yield. Hence, biofuel toxicity is an important issue that needs to be addressed. There are several strategies for addressing biofuel toxicity in microorganisms. Alper et al. [7] employed a global transcription machinery engineering (gTME) approach to improve ethanol tolerance. Stanley et al. [8] used an adaptive evolution engineering method to select stable ethanol tolerant mutants of Saccharomyces cerevisiae, whereas Hou et al. [9] developed novel genome shuffling method to improve biofuel tolerance.
ATP binding cassette transporters (ABC transporters) are transmembrane ion channels found in all organisms. ABC transporters often share common domain architecture with two transmembrane domains (TMD) and two nucleotide binding domains (NBD) that hydrolise ATP or other nucleotides. Pleitropic drug resistance 5 (PDR5) is the most extensively studied ABC transporter from S. cerevisiae. 
Yarrowia lipolytica, a non-conventional oleaginous yeast that efficiently assimilates and utilizes hydrophobic substrates such as alkanes, fatty acids and lipids, was recently used as a model system to study mechanisms of assimilation and degradation of hydrophobic substrates (HS) [12-14]. The characterization of Y. lipolytica mutant, ΔABC1 (YALI0E14729g), with a defective phenotype for hexadecane (C16) utilization, suggested that ABC1 may be involved in import or export of long chain alkanes [15]. Similarly, Y. lipolytica mutant ΔABC2 (YALI0C20265g) showed a decreased cell growth on decane [16]. In addition, genome exploration revealed two homologues, ABC3 (YALIB02544g) and ABC4 (YALIB012980g), which may be also involved in alkane transportation.
Toward the aim of improving alkane tolerance in yeast, classical strain engineering strategies, including mutagenesis and adaptive evolutionary engineering together with genome shuffling and genomic library [17], have been widely used. However, it takes about 6 months to generate ethanol-tolerant mutant by employing the adaptive evolutionary engineering method [8]. Some strategies, are extremely laborious to generate positive mutants. For example, the procedure of yeast genome shuffling, includes EMS treatment, sporulation, spore purification, adequate cross and mutant selection [9]. In addition, for the genomic library approach, more than 10,000 transformants have to form genomic library [17] and be screened. Further, this approach has little room for errors as it needs very high ligation and transformation efficiency. It would require personnel with very good molecular biology techniques. For improvement strategies, such as the random mutagenesis and selection, there is no guarantee about the positive mutant being effective and stable.